This invention relates to snapshot management, such as snapshot acquisition and restoration of data, in a storage system used in a computer system.
A typical example of a storage system of this kind is, for example, a disk system using RAID (Redundant Arrays of Inexpensive Disk) technology. In a storage system of this kind, for example, as a precautionary measure in case of trouble, and to transfer a stored content to other applications, and in connection with debugging, the recording of a snapshot (stored data content at a specific time) of a certain storage region is carried out.
A typical related method of creating a snapshot is a method which uses duplication (mirroring), as set forth in the below-listed Patent Documents 1 and 2. In this method, during normal operation, in which online operations are carried out continually, all updated data is written in duplicate to two volumes. At a designated time, one of the volumes is cut of f from online operations, and the content of this cut off volume is taken as a snapshot of the other volume at the designated time.
Patent Document 1: JP A 2001 306407
Patent Document 2: JP A 2001 331373
With previously proposed snapshot creation methods based on duplication, there has been the problem that, because of the processing burden of constantly duplicating updated data, the response of the storage system to a higher devices falls, and, as a result, the throughput of the computer system as a whole falls.